Dual frequency antenna



Aug. 5,1958 E. c. BEST 2,346,678

DUAL FREQUENCY ANTENNA Filed June 9, 1955 IFF RADAR TRANSMITTER TRANSMiTTER Erhridge C. Besr JNVENTOR. F mg. 4

Nymph? Arforney United States Patent Office 2,845,678 Patented Aug. 5, 1958 DUAL FREQUENCY ANTENNA Ethridge C. Best, Mount Vernon, N. H., assignor, by mesne assignments, to Sanders Associates, Incorporated, Nashua, N. H., a corporation of Delaware Application June 9, 1955, Serial No. 514,286

6 Claims. (Cl. 343-727) This invention relates to directive antennas as used in radar. More particularly, the present invention relates to radar antennas adapted to simultaneously radiate or receive two different frequencies.

In conventional airborne intercept radar systems it is frequently desirable to combine a friend or foe interrogation (IFF) signal with a target search signal utilizing the same antenna. Ordinarily a broader directive pattern is desired for IFF interrogation than the pencil-type beam characteristic of directional searching and tracking systems. An antenna system of the type described is disclosed in U. S. Patent No. 2,653,238, issued to Kenneth P. Bainbridge, September 22, 1953. The present invention is an improvement over Bainbridges dual frequency antenna.

It is, therefore, an object of the invention to provide an improved dual frequency antenna for simultaneously radiating or receiving energy with two different frequencies.

It is a further object of the invention to provide an improved dual frequency antenna having a single reflector adapted simultaneously to transmit or receive signals of two difierent frequencies without mutual interference Another object of the invention is to provide an improved dual frequency antenna having a single, rugged structure.

Other and further objects of the invention will be apparent from the following description of a typical embodirnent thereof, taken in connection with the accompanying drawings.

In accordance with the invention, there is provided an improved dual frequency antenna for simultaneously radiating or receiving signal energies with two different frequencies. The antenna includes a first radiator which is adapted to radiate plane-polarized energy at a first frequency and has a first axis of polarization. A second radiator is provided having a plurality of radiating elements adapted to radiate plane-polarized energy at a second frequency. Polarization of at least one of the elements is non-orthogonal relative to that of the first radiator. Connecting means are adapted to couple the elements to a source of energy and to so phase the energy coupled to each of the elements as to provide a resultant, plane-polarized Wave orthogonally polarized relative to the first axis of polarization.

In one embodiment, the antenna comprises, in combination, a parabolic reflector and a primary radiator which is disposed substantially at the focal point of the reflector. The primary radiator is adapted to radiate polarized microwave energy to illuminate the reflector. The reflector forms a beam of the microwave energy along an axis in a pencil-type radiation pattern. A plurality of radiating elements are each adapted to radiate planepolarized energy of a lower frequency than the microwave energy. The polarization of at least one of the elements is non-orthogonal relative to that of the primary radiator. Supporting means are provided which mechanically connect the primary radiator and the reflector and carry the lower frequency radiating elements. Transmission means are adapted to connect the lower frequency radiating elements to a source of energy and so phase the radiating elements as to provide a resultant, plane-polarized wave orthogonally polarized relative to the microwave energy and to provide directive radiation of the lower frequency energy along the axis. The radiating elements and the primary radiator are adapted, thereby, to radiate the energy of both frequencies simultaneously without mutual interference.

In the preferred embodiment the lower frequncy radiating elements comprise a quadruplet of resonant, cylindrical, dipole antennas. A quadruplet of hollow, supporting rods are angularly disposed relative to the axis and converge toward the primary radiator. The dipoles coam'al- 1y surround and are afiixai to the rods. The parallel Wire transmission line is disposed within the rods and is adapted to connect the dipole antennas in such phase relation as to provide directive radiation.

In the accompanying drawings:

Fig. 1 is a three-dimensional view, partially schematic, of a dual frequency antenna embodying the present invention;

Fig. 2 is a longitudinal section, partially fragmentary, of a support rod in the antenna of Fig. 1;

Fig. 3 is a cross-section of a support rod in Fig. 2 taken along the lines 3-3; and

Fig. 4 is a schematic diagram illustrating an aspect of the operation of the antenna in Fig. 1.

Referring now to the drawings and with particular reference to Fig. 1, a radar transmitter 1 provides a microwave signal, for example 10 kilornegacycles, couples to a solid dielectric, circular Waveguide 2 which is coupled through the center of a circular, paraboloid, metallic reflector 3, formed, for example, of aluminum. The circular guide 2 is coupled to a dielectric radiator 2a which excites a primary radiator within an enclosure 4. The primary radiator is of the form, for example, disclosed and illustrated in co-pending application Serial Number 430,924, filed May 19, 1954, by Jesse L. Butler. The primary radiator is not shown. A metallic reflector 5 directs the microwave energy to illuminate the parabolic reflector 3. A quadruplet of dielectric support rods 6 converge toward the primary radiator as shown and are angularly disposed relative to the principal axis of propagation indicated at 7. Here a reference motor generator 8 is coupled to a shaft 9 which rotates the reflector 5 and the primary radiator within the enclosure 4 to provide conical scanning. The support rods 6 thus effectively mechanically connect the primary radiator and the reflector 3 together. The rods 6 are formed, for example, from circular polystyrene rods of an inch in diameter by 16 inches long. The reflector 3 is typically 24 inches in diameter. The rods 6 carry cylindrical resonant, dipole radiating elements 10 which are one-quarter of a wavelength long at the lower frequency, for example, 500 megacycles, of the energy provided by an IFF transmitter II. The elements 10 are formed, for example of copper, approximately 6 inches long by .001 of an inch thick for use at 500 megacycles. The transmitter 11 is coupled through a parallel wire transmission line 12 to the dipole elements Iltl.

As shown in Figs. 2 and 3, the rods 6 are hollow. The conductors 13 and 14 of the parallel wire transmission line 12 are disposed within the rods and are held in insulated space relation therebetween by a coaxial, dielectric rod 15 aflixed thereto. The conductor 13 is connected to the left-hand dipole element 10, as shown in Fig. 2, through a conductive rod 16. Similarly, the conductor 14 is connected to the right-hand dipole element 19, as shown, through a conductive rod 17.

The operation of the invention will now be described 3 with particular reference to Fig. 4. The primary radiator is adapted to radiate plane-polarized microwave energy in a direction of polarization as indicated at 18, at a frequency, for example, of kilo-megacycles.

It will be apparent, from the instantaneous polarities of the elements 10, as shown, that the IFF radiation pattern of the preferred embodiment, is quite broad. The lower frequency energies having a plane of polarization as indicated by the dashed arrow 19, combine in phase in both the horizontal and vertical polarization axes; the resultant lower frequency energy is thus maximum along the central axis of the parabolic reflector 3. The horizontally polarized lower frequency, energy cancels along the axis 7 and in the horizontal and vertical polarization axes. The central axis of the reflector 3 coincides with the maximum propagation axis 7 of the microwave energy. It will be apparent that the great difference in frequencies between the frequency of the microwave energy and the lower frequency energy substantially aids in precluding mutual interference therebetween.

The problem of microwave energy interfering in the lower frequency channel is readily overcome by inserting a low-pass filter in the lower frequency channel; Such interference may also beprecluded by suitably adjusting the plane of polarization of the input lower frequency energy relative to that of the microwave energy. This may be accomplished by exciting only a pair of lower frequency radiators that are vertically, co-linearly disposed.

The present invention has particular application to airborne radar systems wherein maximum compactness and minimum weight are an essential requirement.

While there has been hereinbefore described what is at present considered a preferred embodiment of the invention, it will be apparent that many and various changes and modifications may be made with respect to the embodiment illustrated without departing from the spirit of the invention. It will be noted, therefore, that all such changes and modifications as fall fairly Within the scope of the present invention, as defined in the appended claims, are to be considered as a part of the present invention.

What is claimed is:

l. A dual frequency antenna for simultaneously radiating or receiving energy of two different frequencies comprising, in combination, a parabolic reflector; a primary radiator disposed substantially at the focal point of said reflector and adapted to radiate polarized microwave energy to illuminate said reflector, said reflector forming a beam of said microwave energy along an axis in a pencil-type radiation pattern; a plurality of radiating elements each adapted to radiate plane-polarized energy of a lower frequency than said microwave energy, the polarization of at least one of said elements being non-orthogonal relative to that of said primary radiator; a supporting means mechanically connecting said primary radiator and said reflector and carrying said lower frequency radiating elements; and transmission means adapted to connect said lower frequency radiating elements to a source of lower frequency energy and sophase said radiating elements as to provide a resultant, plane-polarized wave orthogonally polarized relative to said microwave energy and to provide directive radiation of said lower frequency energy along said axis, said radiating elements and said primary radiator being adapted, thereby, to radiate said energy of both said frequencies simultaneously without mutual interference.

2. A dual frequency antenna for simultaneously radiating or receiving energy of two different frequencies comprising, in combination, a parabolic reflector; a primary radiator disposed substantially at the focal point of said reflector and adapted to radiate polarized microwave energy to illuminate said reflector, said reflector forming a beam of said microwave energy along an axis in a pencil-type radiation pattern; a plurality of radiating 4 elements each adapted to radiate plane-polarized energy of a lower frequency than said microwave energy, the polarization of at least one of said elements being nonorthogonal relative to that of said primary radiator; a. plurality of supporting rods mechanically connecting said primary radiator and said reflector and carrying said lower frequency radiating elements; and transmission line means adapted to connect said lower frequency radiating elements to a source of lower frequency energy and so phase said radiating elements as to provide a resultant, plane-polarizedwave orthogonally polarized relative to said microwave energy and to provide directive radiation of said lower frequency energy along said axis, said radiating elements and said primary radiator being adapted, thereby, to radiate said energy of both said frequencies simultaneously without mutual interference.

3. A dual frequency antenna for simultaneously radiating or receiving energy of two different frequencies comprising, in combination, a parabolic reflector; a primary radiator disposed substantially at the focalpoint of said reflector and adapted to radiate polarized microwave energy to illuminate said reflector, said reflector forming a beam-of said microwave energy along an axis in a pencil-type radiation pattern; a plurality of. dipole radiating elements each adapted to radiate energy of a lower frequency than said microwave energy, at least one of said dipole elements being angularly disposed relative to said axis and polarized non-orthogonally relative to said primary radiator; a plurality of supporting rodsmechanically connecting said primary radiator and said reflector and carrying said dipole elements; and transmission line means adapted to connect said dipole elements to a source of lower frequency energy and so phase said dipole elements as to provide a resultant, plane-polarized wave orthogonally polarized relative to said microwave energy and to provide directive radiation of said lower frequency energy alongsaid axis, said radiating elements and said primary radiator being adapted, thereby, to radiate said energy of both said frequencies simultaneously without mutual interference.

4. A dual frequency antenna for simultaneously radiating or receiving energy of two different frequencies comprising, in combination, a parabolic reflector; a pri mary radiator disposed substantially at the focal point of said reflector and adapted to radiate polarized microwave energy to illuminate said reflector, said reflector forming a beam of said microwave energy along an axis in a pencil-type radiation pattern; a plurality of radiating elements each adapted to radiate energy of a lower frequency than said microwave energy, the polarization of at least one of said elements being non-orthogonal relative to that of said primary radiator; a plurality of hollow, dielectric, supporting rods mechanically connecting said primary radiator and said reflector and carrying said lower frequency radiating elements; and transmission line means disposed within said rods and adapted to C011. nect said lower frequency radiating elements to a source of lower frequency energy and so phase said radiating elements as to provide a resultant, plane-polarized wave orthogonally polarized relative to said primary radiator and to provide directive radiation of said lower frequency energy along said axis, said radiating elements and said primary radiator being adapted, thereby, to radiate said energy of both said frequencies simultaneously without mutual interference.

5. A dual frequency antenna for simultaneously radiating or.receiving energy of two different frequencies comprising, in combination, a parabolic reflector; a microwave generator providing a source of energy in the microwave frequency range; a lower frequency generator providing energy at a lower frequency than said microwave frequency range; a primary radiator disposed substantially at the focal'point of said reflector and adapted to radiate polarized microwave energy'to illuminate said reflector, said reflector forming a beam of said microwave energy along an axis in a pencil-type radiation pattern; a quadruplet of resonant, cylindrical, dipole antennas adapted to radiate energy of a lower frequency than said microwave energy and with a resultant plane of polarization perpendicular to the polarization plane of said microwave energy; transmission line means connecting said microwave generator to said primary radiator through the center of said reflector; a quadruplet of hollow, dielectn'c, supporting rods, angularly disposed relative to said axis and converging toward said primary radiator, to mechanically connect said primary radiator and said reflector, said dipoles coaxially surrounding and afiixed to said rods, each of said dipoles being non-orthogonally polarized relative to said primary radiator; and a parallel Wire transmission line disposed within said rods and adapted to connect said lower frequency generator to said dipole antennas in such phase relation as to provide a resultant, plane-polarized wave orthogonally polarized relative to said microwave energy and to provide directive radiation of said lower frequency energy along said axis, said dipole antennas and said primary radiator being adapted, thereby, to radiate said energy at both said frequencies without mutual interference.

6. A dual frequency antenna for simultaneously radiating or receiving energy with two different frequencies, comprising: a first radiator adapted to radiate planepolarized energy at a first frequency and having a first axis of polarization; a second radiator having a plurality of radiating elements adapted to radiate plane-polarized energy at a second frequency, the polarization of at least one of said elements being non-orthogonal relative to that of said first radiator; and connecting means adapted to couple said elements to a source of energy and to so phase the energy coupled to each of said elements as to provide a resultant, plane-polarized wave orthogonally polarized relative to the first said axis of polarization.

References Cited in the file of this patent UNITED STATES PATENTS 2,653,238 Bainbridge Sept. 22, 1953 FOREIGN PATENTS 144,183 Australia Dec. 27, 1935 475,855 Great Britain Nov. 26, 1937 

